The present invention relates in general to a storage device system, and, more particularly, the invention relates to a technique for carrying out copying from one storage device system to another storage device system in a bi-directional manner.
In an information system having a host computer operating as a superior device and a plurality of storage device systems (storage systems), a remote copy function is used as a technique for carrying out data copying between storage device systems. The remote copy function involves the copying of data between a plurality of storage device systems which exist at physically remote locations, without intervention of a superior device, in an information processing system, i.e., a technique for carrying out double writing. The storage device system in this case in a system which is configured by a plurality of storage devices and a controller for controlling those storage devices. In an information processing system for carrying out the remote copy function, storage device systems which are disposed respectively at physically remote locations are mutually connected by a dedicated line or a public line. The dedicated line or the public line which is used for this connection is called a remote copy line.
Among the logical storage regions (hereinafter referred to as a “logical volume”) provided in a certain storage device system, a logical volume of the same capacity as the capacity of a logical volume which becomes an object of a remote copy (hereinafter referred to as a “copy-source logical volume”) is secured in another storage device system for copying the same. This secured logical volume (hereinafter referred to as a “copy-destination logical volume”) is formed so as to have a one-to-one relationship with the copy-source logical volume (hereinafter referred to as a “copy pair”). Data of the copy-source logical volume is copied to the copy-destination logical volume through a dedicated line or a public line. In the case of an updating of data which is included in the copy-source logical volume, updated data is transferred through the dedicated line etc. to a storage device system having the copy-source logical volume, and the updated data is also written into the copy-destination logical volume which corresponds to the copy-source logical volume. Using this remote copy technique, in an information processing system having a plurality of storage device systems, it is possible to hold logical volumes to hold the same data contents in a plurality of storage device systems.
By forming a copy pair consisting of a copy source and a copy destination, the copy direction from the copy source to the copy destination is determined to be in one direction. As to the copy-source logical volume, it is possible to carry out a write-in process from a superior device. Adversely, as to the copy-destination logical volume, it is impossible to carry out a write-in process to a superior device.
Supposing that the copy direction is not fixed to one direction and data write-in to a storage device system which configures the copy pair is enabled, it is impossible to hold identical contents of data in respective storage device systems. This is because of the transfer time which is required for transfer of copy data when a superior device carries out write-in to a storage device, and, thereafter, a data content to be written is written into a storage device as the copy destination.
An environment in which a copy pair is formed between a storage device system A and a storage device system B will be described more specifically as an example. Here, the storage device system A and the storage device system B are sufficiently spaced from each other geographically, that it takes, for example, 1 second and more until data is written into the storage device system A from a superior device, and, then, double data is transferred and written into the storage device system B from the storage device system A.
Here, supposing that, at almost the same time, different data contents (content A, content B, respectively) were written into the same regions of the storage device system A and the storage device system B from a superior device, the content A and the content B are written into the storage device system A and the storage device system B, respectively. After the respective data write-ins have been completed, at almost the same time, from the storage device system A to the storage device system B, as well as from the storage device system B to the storage device system A, the content A and the content B are transferred. In such a situation, after the storage device system A and the storage device system B have received the transferred data, the content A and the content B should have been overwritten in the storage device system A and the storage device system B, respectively. In the storage device system A, a situation occurs in which the content B is overwritten on the content A, and in the storage device system B, a situation occurs in which the content A is overwritten on the content B. In such a case, the data contents which were written into the storage device system A and the storage device system B become different, which results in the fact that duplication of the volume has not been carried out.
In order to avoid such a situation and to realize complete duplication of the volume, a copy direction is set to be one direction like from the copy source to the copy destination. The technology regarding this type of remote copy function is disclosed in U.S. Pat. No. 5,742,792 (Patent Document 1).
Up to now, a storage device which is shared by a plurality of superior devices, on the basis of a shared exclusive control request from an arbitrary superior device, realizes a shared exclusive control to an access request from an individual superior device. For example, in an information system which adopts a SCSI (Small Computer System Interface) as an interface between a superior device and a storage device, by use of a reserve series command which is defined by the SCSI, it is possible to realize the shared exclusive control with a logical volume unit of the storage device. On the occasion that a certain superior device has reserved the logical volume, a situation occurs in which read-access and write-access become possible only from the reserved superior device.
In the SCSI reserve series command, there is also an extension command by which the shared exclusive control can be carried out with a block unit of a disk. A SCSI command for reserving a partial region (extent) on this logical volume is defined as an extent reserve (hereinafter referred to as a “region reserve”). A region to be reserved has a reserve attribute. The reserve attribute enables read-share, exclusive-write, exclusive-read, and exclusive access operations. The technology regarding SCSI-2 is described in an item 6.15 of SCSI-2 DETAIL COMMENTARY, Volg. 3, published by CQ Publishing Co., Ltd. on Feb. 1, 1997 (Non-Patent Document 1).
Under the current remote copy technology environment, a shared exclusive control mechanism performed by the reserve series command of a SCSI has not been considered, and even on the occasion in which the logical volume in a certain storage device system is locked by the reserve command, the locked state is not transmitted to a remote copy corresponding logical volume in another storage device system.
This creates a problem in that the remote copy function of the above-described related art enables writing only into the copy-source logical volume from a superior device. Also, there is a problem in that the locked state produced by the reserve series command is not transmitted to the remote copy corresponding logical volume.